(Disclaimer: these are lecture outlines with some figures; these are not lecture notes)
 

MATTER IN WATER

• Total dissovled (filtrable) solids - solids that pass through a GFC filter (pore size 0.8 µm)
• Total suspended (nonfiltrable) solids - solids that are retained on a GFC filter
• settable solids (w/in 1 h)
  
• non-settable suspended solids
  In still water:

Clay <2 µm 14 days to sink 5 cm water Silt 2-20 µm 3.5 days Sand 20-2000 µm 1.5 second

But in aquatic systems, the rate of settling also depends on the mechanical energy of the water (water movement)

  Overlap:

Both dissolved and suspended solids can be measured gravimetrically
Which is likely to weigh more in an typical surface freshwater sample?
Which is more likely to interfere with light transmission through water?

 

Much of the fraction that is dissolved, can be estimated by conductivity (specific conductance) - the capacity of a solution to conduct electrical current. Estimates total dissolved

 


Much of the fraction that is suspended, can be estimated by measuring light properties.
Given this, will suspended solids affect  temperature in natural waters?
 


 
 
 

The amount of organic matter in water can be estimated as biochemical oxygen demand (BOD) or chemical oxygen demand (COD)

• Angle of incidence

• Cloud conditions

• Surface waves

• Ice

* Scattering - suspended particles reflect light at a massive array of angles
 
 
 

* Absorption - diminution of light by transformation into heat energy
 
 

 

 

Light entering pure water:

* longer visable light (reds) absorbed shallower

* shorter wavelengths (blues) tend to scatter

 

Light entering lake water with other matter:

* organic compounds - often absorb blues and greens

* silts and clays - reds and oranges more likely to be scattered - how do color and clarity differ from water with high  concentrations of organic compounds?

* phytoplankton chlorophyll - What color is not absorbed by Chl a?

 

 Measuring light properties in water (usefulness depends on question asked):
    

Turbidity - an expression of the optical properties that cause light to be scattered and absorbed rather than transmitted in a straight line. Turbidity is primarily caused by total suspended solids but a direct relationship is varies from system to system. Why?

Nephlometer (turbidometers) measures intensity of light scattered at 90°.
 
 
 

Vertical illumination (light penetration) - illumination at some depth as measured by underwater photometer. Light is absorbed exponentially with depth (a constant percentage of light available is extinguished at each meter)
  I_z = I_o e^-kz where: I_o = intensity of light at surface
I_z  = intensity of light at depth z in meters
k = vertical absorption coefficient <>
When plotted as depth vs log % incidence of light, line is straight in a homogeneous solution.
   

What would a deflection in the line indicate?
 
 

Compensation depth - Respiration exceeds photosynthesis within a cell at about 1% of incident surface light (the photic zone is the region from the surface to where 99% of light has disappeared).
 
 
 

 
 
 

Visibility - measure of the depth at which one can see into the water. Measured using a secchi disc.  
What factors affect this measurement?

Visibility can be used to estimate photic depth and trophic state
What factors affect these estimate?
 

http://dipin.kent.edu/secchi.htm           http://www.hao.ucar.edu/public/education/sp/images/secchi.html

 * langmuir spirals
 
 

* seiches
 
 

* internal waves

 
 
 

 

http://wow.nrri.umn.edu/wow/under/primer/page5.html

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